If its pounding the flooer and everything else at mid vol level, then the subs vol is set way too high. At the moment Im listening to music at a high vol level, and even tho I can feel the bass through my body but its not shaking everything else, unless the frequencies get real low, hehe.
A sub is deff a improvement whatever vol level you like to listern at. Why do ppl think that a sub is only any good at high vol level, yeh you can feel it better at high vol, but that doesnt mean al low vol it wont benefit, cos it will.
1. Takes some of the load off the speakers equalling in a clearer sound as I keep saying.
2. will be able to produce the lower frequencies much better then you speakers can, at low or high vol level.